Ring-bromination of toluene using small amounts (10-20 mole %) of transition metal halide catalysts has been used to prepare monomeric flame retardants for polymers such as ABS resins and polypropylene. While attempting to ring-brominate benzyl bromide using a AlCl.sub.3 catalyst in bromine, it was unexpectedly found that the primary product was a novel, ring-brominated polymer, poly(tetrabromobenzylbromide). Polymeric flame retardants have several desirable properties such as non-blooming character and generally good UV stability, which is not always the case with monomeric flame retardants.